Process of forming minute capsules and three-phase capsule-forming system useful in said process

ABSTRACT

A process is disclosed for manufacturing minute capsules, en masse, in a liquid manufacturing vehicle wherein the capsules contain water or aqueous solutions. The capsules have seamless walls of a specific kind of hydrophobic polymeric material which polymeric material has been found particularly impervious to permeation and diffusion by the aqueous contents. The hydrophobic polymeric material used is poly(ethylene-co-vinyl acetate) having the vinyl acetate groups hydrolyzed to vinyl alcohol groups in the amount of 38 to 55 percent.

United States ateut [is] 3,674,704 Bayless et al. July 4, 1972 [54]PROCESS OF FORMING MINUTE [56] References Cited EZ 23ifi i iiiiiiiifiiismL STATES TENTS [N SAID PkOCESS 2,702,264 2/1955 Klaui ..424/333,415,758 12/1968 Powell et al. ..252/3 I6 [72] Inventors: Robert G.Bayless; Charles P. Shank; Ruth 3,423,489 [/1969 Arens et al ..264/4 A.Botham; l)ennis W. Werkmeister, all of Daymn Ohm PrimaryExaminer-Richard D. Lovering [73] Assignee: The National Cash RegisterCompany, Attorney-E Frank McKinney and Robe" Shafel' Dayton, Ohio [22]Filed: March 29, 1971 [57] ABSTRACT [21] APP] NOJ 128 670 A process isdisclosed for manufacturing minute capsules, en

masse, in a liquid manufacturing vehicle wherein the capsules containwater or aqueous solutions. The capsules have seam- U-S. M, less wallsofa pecific of hydrophobic polymeric material 7/622, 117/100 117/109264/4 424/33 which polymeric material has been found particularlyimpervi- [51] lllt. Cl. ..B01j 13/02, B44d 1/02 ous to permeation anddiffusion y the aqueous contents- The [5 8] held of Search "252/316; 117/100 ii g hydrophobic Polymeric material used is Poly(ethylene-covinylacetate) having the vinyl acetate groups hydrolyzed to vinyl alcoholgroups in the amount of 38 to 55 percent.

8 Claims, 1 Drawing Figure IMPROVING CAPSULE QUALITY I I I 1 l l lINCREASING HYDROLYSIS OF VINYL ACETATE P A'TENTEUJUL '4 m2 54%INCREASING HYDROLYSIS OF VINYL ACETATE IMPROVING CAPSULE QUALITY PROCESSOF FORMING MINUTE CAPSULES AND THREE-PHASE CAPSULE-FORMING SYSTEM USEFULIN SAID PROCESS BACKGROUND OF THE INVENTION 1. Field of the InventionThe present invention relates to minute capsules having hydrophobicpolymeric wall material and containing water, aqueous solutions or watersoluble materials. A process is disclosed for manufacturing thecapsules, en masse, in a liquid vehicle. The capsule wall material ispartially hydrolyzed poly(ethylene-co-vinyl acetate) and a particularlyimportant feature of the invention resides in the discovery that thedegree of hydrolysis of the polymeric capsule wall material is criticaland that only a narrow range of materials is eligible for use. It shouldbe noted that any reference hereinafier to poly(ethylene-co-vinylacetate) means partially hydrolyzed poly(ethylene-co-vinyl acetate),unless otherwise specified.

The present invention embraces a specific process for manufacturingminute capsules wherein the capsule wall material is narrowly specifiedand wherein the capsules contain particular aqueous or water solublecompositions. The capsules are substantially spherical and are minute"in size, which means that the capsules have average diameters of fromabout a few microns to several thousand microns.

2. Description of the Prior Art US. Pat. No. 3,415,758 issued Dec. 10,1968 on the application of Thomas C. Powell et al. and assigned to theassignee herein discloses and claims a process for manufacturing minutecapsules, en masse, in a liquid manufacturing vehicle. The encapsulatingprocess of that patent utilizes liquid-liquid phase separation ofhydrophobic polymeric capsule wall material by addition of aphase-separation-inducing agent to a solution of the wall material. Theencapsulated material must be insoluble in the capsule manufacturingvehicle and is generally water soluble. A general encapsulating processis taught by the Powell et al. patent. An encapsulating process is nottaught therein with respect to the specific materials required inpractice of the present invention to afford an improved product.

The capsules in that Powell et al. patent contain aqueous and watersoluble compositions and the capsule wall material is disclosed to behydrophobic polymeric material having water-wetting groups attachedthereto. Although the aboveidentified patent discloses hydrophobicpolymeric capsule wall materials, in general, there is no mention of thematerial now discovered and herein disclosed to be especially useful incontaining aqueous compositions.

SUMMARY OF THE INVENTION The preferred capsule-forming process of thisinvention involves the establishment of an encapsulating system which ischaracterized as follows (these terms being defined below):

1. It is un-ionized;

2. It is in an agitated state;

3. It comprises the following three phases characterized first of all bybeing mutually immiscible and further characterized, respectively, asbeing:

a. a continuous liquid phase vehicle that constitutes at least about 75percent by volume of the three phases in total,

b. a discontinuous phase of minute, mobile entities of intended capsulecore material, either solid or liquid, including water or water-likeliquids, dispersed in the vehicle and constituting less than about 25percent, by volume, of the three phases in total, and

a discontinuous phase of minute, mobile entities of wall-formingmaterial dispersed in the vehicle and constituted by a solution ofpartially hydrolyzed poly(ethylene-co-vinyl acetate) hydrophobicpolymeric material.

The present invention is particularly concerned with the discovery thatif the hydrophobic polymeric material used in practice of the presentsystem to produce the capsule walls is hydrolyzed to a certain,predetermined, degree, the capsule walls exhibit improvedcharacteristics with respect to permeability and other physicalqualities.

The un-ionized, agitated, encapsulating system using such polymericpoly(ethylenc-co-vinyl acetate) material results, without more, in adeposit of the wall-forming material around the dispersed entities ofintended capsule core material, such as water, aqueous solutions orwater soluble materials therein. By reason of the viscosity and volumerelation of the dispersed phase of wall-forming polymer solution, thatphase is capable of deposit around the dispersed entities of intendedcore material and is also capable, after deposit, of maintaining itselfas an embryonic wall against the shearing forces that exist as anincident of the required agitation of the system. The deposits quicklyaccumulate to a maximum thickness, which thickness may be varied byvarying the amount of the wall material provided and the degree and typeof agitation used. The amount of capsule wall material required ordesired may vary in accordance with the need for protection of thecapsule core material and the protective characteristics of thewallforming material selected for use.

Depending on the nature of the core material and on that of the wallmaterial, the capsules initially formed in the liquid vehicle by thissystem are more or less durable. Various supplemental treatments of thecapsules so-formed may optionally be employed to harden the capsulewalls and thereby impart to them, among other properties, greaterdurability and greater impermeability relative to the core material andto the environment.

The present process for making capsules, en masse, in a liquid vehicleby establishing a system as defined above, differs from the prior artprocesses in that the specific polymeric material for capsule walls ofthe present invention is different from materials disclosed in the priorart, and differs particularly in that the polymeric material ishydrolyzed to a specific and particular degree thus yielding improvedcapsules. This process using the special wall materials having the notedcharacteristics is applicable to the encapsulation of a wide range ofcore materials, including many that cannot be suc cessfully encapsulatedand contained by processes described in the prior art; and this processis particularly capable of encapsulating water and water-like liquidcore materials as well as solid water-sensitive materials in solution.

Some of the criteria which define the useful classes of materials forthe vehicle and the wall-forming solution are these: (1) The hydrophobicpolymeric material of the wallforming solution must bepoly(ethylene-co-vinyl acetate) hydrolyzed to a particular, specified,degree with respect to the vinyl acetate moiety. (2) The solution ofpolymeric materials which form the capsule wall must be capable ofwetting the core material in order to deposit around the capsule coreentities. (With further regard to wetting properties, thepoly(ethylene-covinyl acetate) has hydroxyl and acetate groups, thewetting properties of which in certain instances may be enhances by thesolvent). (3) The phaseseparated solution of the poly(ethylene-co-vinylacetate) material should have a viscosity, preferably about 1,000 to4,000 centipoises, such that it may deposit itself and maintain itselfdeposited around the capsule core entities, despite shearing forces ofagitation required to maintain a dispersion. (4) The phase-separatedsolution of copolymer material should constitute such a percentage ofthe total three-phase system, by volume, preferably less than about 5percent, that it can exist as a dispersed phase of mobile entitiescapable of deposit around the core entities. (5) The core material, thesolution of copolymer, and the vehicle must be mutually immiscible andchemically inert toward each other.

As previously stated, the capsule wall material for use in the presentinvention is a partially hydrolyzed derivative of a copolymer ofethylene and vinyl acetate-named poly(ethylene-co-vinyl acetate). Somevinyl acetate moieties of each molecule are hydrolyzed to yieldpolymeric molecules having ethylene groups, vinyl acetate groups andvinyl alcohol groups. It has been discovered that poly(ethylene-co-vinyl acetate) is especially effective as capsule wallmaterial in the present invention when the vinyl acetate content hasbeen partially hydrolyzed to a particular, predetermined, content ofvinyl alcohol. The reason for such effectiveness is not entirelyunderstood; but, as will be demonstrated in Examples below, theeffectiveness is certainly manifest. A structural representation of thecompound used in this invention is wherein x, y and z represent molfractions of ethylene, vinyl alcohol and vinyl acetate, respectively. Inunhydrolyzed polymeric material there can be discussed a mol fraction ofethylene and vinyl acetate; and such a fraction can also be applied tothe partially hydrolyzed capsule wall material of this invention. In thecase of this invention, however, the fraction is that of ethylene groupsto the total of ethylene groups, vinyl acetate groups and vinyl alcoholgroups, combined, or the mol percent of ethylene groups present. Thatratio for materials used in this invention can be from 0.70 to about0.85;about 0.75 to 0.85 being preferred and about 0.80 being mostpreferred.

Poly(ethylene-co-vinyl acetate) must be hydrolyzed to a particularextent for use in the present invention. Vinyl acetate groups arehydrolyzed to vinyl alcohol groups and it has been discovered that from38 to 55 percent of the vinyl acetate groups must be hydrolyzed toprovide the improved capsule wall material. In the most preferred case,referring to the structural representation above, x (ethylene) equalsabout 0.80, y (vinyl alcohol) equals about 0.075 to 0.105, and 2 (vinylacetate) equals about 0.095 to 0.125. For reasons not entirelyunderstood, poly(ethylene-co-vinyl acetate) is not eligible for use inthis invention wherein the vinyl acetate is hydrolyzed in an amount lessthan about 38 percent or more than about 55 percent. The most preferredlimits of hydrolysis of the vinyl acetate to vinyl alcohol is about 43to 53 percent.

What is believed to be important and patentable and to represent anunobvious advance in the art in the present invention resides in thediscovery that a particular polymer provides improved capsulecharacteristics in manufacture of minute capsules. Partially hydrolyzedpoly(ethylene-co-vinyl acetate) has been discovered to be an especiallyeffective capsule wall material when about 38 to 55 mol percent of thevinyl acetate has been hydrolyzed to vinyl alcohol groups. The partiallyhydrolyzed polymeric material eligible for use in this invention has,generally, a molecular weight of about 50,000, more or less;themolecular weight not being of critical importance except that if it istoo great the polymer will be relatively insoluble in the system and ifit is too low there may be some difficulty in the physical character ofthe separated phase. Material having a wide range of molecular weightsis eligible for use. The stated criterion that the core material, thepolymer solution, and the vehicle be mutually immiscible is used in theordinary sense that their separate existence in the system must not beimpaired by any reactivity or miscibility between them.

Prefabricated systems for use in carrying out the process of thisinvention may be established and stored for future use. Even unskilledoperators may complete such systems by the addition of missing materialalong with agitation and heat, if necessary, together with agencies forhardening of the capsule walls, to make capsules at a later time. Themissing material may involve any of those three necessary to form anoperative system, and the absence of any component may be total orpartial.

The preferred system, utilizing the specified poly(ethyleneco-vinylacetate) materials, is one in which the liquid used as the solvent forthe wall-forming material is also used as a major component of themanufacturing vehicle. The vehicle then must contain another material,in solution in it, which material is complementary to the wall-formingmaterial in the sense that it creates an immiscibility between thevehicle and the solution of wall-forming polymeric material and inducesa liquid-liquid phase separation. In other words, it completes a liquidsystem in which the suitably-viscous wall-forming solution ofpoly(ethylene-co-vinyl acetate) material can exist as a separate phasedispersed in the vehicle because of forces between the polymericmaterial of the wall-forming solution and the complementary material.Without the complementary material, if the vehicle included or consistedof the same liquid that is used as the solvent for the wall-formingpolymer, the vehicle would be miscible with and would dilute the polymersolution, which then would not exist as a separate phase of properviscosity. Thus, the stated immiscibility between the vehicle and thewall-forming polymer solution requires the presence of a complementarymaterial as a constituent of the vehicle when the vehicle includes aliquid miscible with or identical to the solvent used in thewall-forming solution.

Complementary materials for use in the present invention include suchdiverse polymers as: polybutadiene (8,000-l0,000 molecular weight);polybutene (330-780 molecular weight); polydimethyl siloxane; cottonseedoil, linseed oil, soya oil, and other vegetable oils and mineral oils,either halogenated or not; and the like. The general process ofliquid-liquid phase separation is taught by the prior art andcomplementary materials, generally, taught as eligible therein areuseful, also, here. Kind and type of complementary material is notconsidered to be a part of the present invention. The complementarypolymeric material used in the present encapsulating system can be anypolymer that has less affinity for the core material than does theoly(ethylene-co-vinyl acetate) capsule wall material, so that thecapsule wall material will deposit preferentially around the coreentities.

While encapsulating systems utilizing the oly(ethylene-covinyl acetate)are particularly useful in the encapsulation of materials selected fromthe class comprising water, aqueous solutions, hydroxy-containingcompounds, polyhydroxy-containing compounds, aqueous solutions ofhydroxy and polyhydroxy compounds, and solutions and dispersions ofsolids therein, they are also capable of encapsulating solid materialssuch as, for example, titanium dioxide, potassium penicillin, sodiumchloride, aspirin, methylene blue, pepsin, starches, methyl cellulose,and gelatin, as well as any other materials which are not reactive orsoluble with other phases of the three-phase system in order to maintaintheir existence. Particular materials especially eligible to becontained in capsules of this invention are formamide, glycerine,glycols, amines such as triethylenetetramine, diethylenetriamine,aminoethylethanolamine, diethyleneamine and the like, and carbonatessuch as ethylene carbonate, propylene carbonate and the like. Mixturesof any of the foregoing core materials in the same core entity or asproviding diflerent core entities in the same threephase system may beused. Materials particularly intended as capsule core materials hereinmust, of course, be substantially immiscible with other components ofthe encapsulating system.

The size range of capsules made by the present invention can extend froma lower limit of a few to several microns up to a larger limit ofseveral thousand microns in average diameter. The usual size forcapsules made according to the present process are from about I or 2microns to about 15,000 microns in average diameter. Capsules of theaforementioned size are considered to be minute and are preferred. Themost usual size for capsules manufactured according to the presentinvention is within a range of from about 5 microns up to about 2,500microns. Capsules made according to the present invention can be made tocontain a range of amounts of internal phase material. The capsules cancontain from 0 to more than 99 percent, by weight, of the internal phasematerial. The most usual and preferred range for the amount of materialto be contained in capsules manufactured according to the presentinvention is from about 50 to about 97 percent, by weight. Theaforementioned capsules having zero contents are considered to be minutespheres of polymeric material and can be manufactured by the process ofthe present invention by omitting the intended internal phase material.Hollow capsules can be manufactured, wherein the initial capsulecontents are removed.

Solvents eligible for use in this invention include organic solventswhich can dissolve both the poly(ethylene-co-vinyl acetate) and thecomplementary phase-separation-inducing material. The solvents aregenerally well-known, or are easily found without undue experimentation,and include: cyclohexanol; methylisobutyl ketone; trichloroethylene;tetrachloroethylene; methylene chloride; carbon tetrachloride;chloroform; toluene; xylene; benzene; chlorobenzene; ethylene glycolmonobutyl ether; l-methyl-2-pyrrolidinone; pyridine; butanol and thelike. Kinds and types of particular eligible solvents is not consideredto be a novel part of the present invention.

In order to more completely exPlain the invention, a particularprocedure for establishing a suitable encapsulating system will bedescribed. This particular procedure involves the formation of anun-ionized solution system comprising two different polymeric materialsand a common solvent;one polymeric material being thepoly(ethylene-co-vinyl acetate) capsule wall material and the otherpolymeric material being the complementary phase-separation-inducingmaterial. Separation of this system into two separate liquid solutionphases (one containing a major amount of the poly(ethyleneco-vinylacetate) and the other containing a major amount of the complementarypolymeric material) is accomplished by a phenomenon of liquid-liquidphase separation known from the work of Dobry et al. published inJournal of Polymer Science," Vol. 2, No. 1, pp. 90-100 (1947). The twopolymeric materials and the solvent can be assembled in any order toeffect the phase separation, but it is preferable first to form a dilutesolution of the poly(ethylene-co-vinyl acetate) that is intended to bein the capsule-wall-forming phase, and then to induce liquid-liquidphase separation by addition of the complementary, polymeric material,whose only role is to induce and maintain the phase separation.

The order of addition can be reversed, or the two polymeric materialsand the solvent can be brought together at one time, once the properquantitative relations are established for the particular materialsbeing used. The resulting volume and viscosity (mostly as it iscontrolled by concentration) of the two separate phases are independentof the order of assembly.

The core material, always a minor component of the total volume of thesystem, can be added before, during or after the formation of thesolution or its separation into two solution phases. Similarly, theagitation of the system can be begun before, during, or after either ofthese steps. It is preferred, however, to agitate before, during, andafter the phase separation, and to introduce the core material beforethe phase separation has taken place.

The intensity of agitation is made such as to reduce the core materialto the desired entity size, if such is necessary, and, in any event, toassure thorough dispersion of it in the vehicle. The core entity size ispre-selected to give the desired capsule size after allowance forencapsulating wall thickness. With solid core materials, the entity sizecan be predetermined and obtained by suitable grinding or milling.

When the three-phase capsule-forming system is established in this way,the continuous or vehicle phase consists of a more dilute and lessviscous solution containing the greater part of the complementarypolymeric material; and that polymeric material is the material whichimparts the necessary immiscibility between the vehicle and thewall-forming solution phase and permits the latter to exist as aseparate dispersed phase. Any small amount of complementary polymericmaterial that may pass into the separated wall-forming solution phase byentrainment or otherwise is not objectionable.

lfdesired or required, the three-phase system, once containing capsules,may be treated with a small amount of some compound which will reactwith hydroxy groups in the capsule wall material to chemically hardenand cross-link the capsule walls. Preferred amongst the hardening ortreatment materials are diisocyanate or polyisocyanate materials such astoluene diisocyanate and diacid halides such as malonyl-chloride, oxalylchloride, sulfonyl chloride, thionyl chloride, and the like. Anothermethod for treating the capsule walls is by reaction with an alkalialkoxide, the mechanism of which reaction is not entirely understood.Examples of alkali alkoxides include sodium, potassium, lithium andcesium methoxide, ethoxide, propoxide, and the like.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE is a subjective graphicalrepresentation of the relation between capsule quality and percenthydrolysis as applied to the poly(ethylene-co-vinyl acetate), partiallyhydrolyzed. For reasons not entirely understood, the change in qualitywith change of percent hydrolysis is quite pronounced and remarkable. Athydrolysis of less than about 38 percent, the separated phase preparedaccording to established liquid-liquid phase separation techniques, isnot adequately viscous to form useful capsule walls and what walls whichare formed are sticky and generally unmanageable in attempts to isolatethe capsules. Capsules made using materials having less than 38 percenthydrolysis have a tendency to agglomerate during the encapsulationprocess and lack of vinyl alcohol groups prevents adequate cross-linkingacross hydroxyl groups.

At hydrolysis of greater than about 55 percent, the separated phase istoo viscous and exists as a semi-solid, stringy, precipitous phase. Thechange from good to "no-good" is abrupt and appears to be completewithin a few percent.

At hydrolysis between 38 and 43 percent, capsules of adequate qualitycan be prepared with the quality improving as 43 percent hydrolysis isapproached.

Between 43 and 53 percent hydrolysis the capsule equality is at amaximum for this system and the capsules are particularly suited forcontaining polar liquids for long periods of time.

From hydrolysis of 53 to 54 or 55 percent, capsule quality declinesrapidly and, a hydrolysis of about 56 percent capsules, can no longer besuccessfully manufactured.

DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE I In this example,minute capsules will be manufactured which contain glycerol as a polarinternal phase. If desired or required, the glycerol can have some smallamount of dye or other coloring material dissolved or dispersed thereinfor demonstrative effect or for some other purpose. The capsulewall-forming polymeric material used in this example and in all of thefollowing examples is poly(ethylene-co-vinyl acetate) hydrolyzed to aparticular percent as hereinabove described. Each example will specifythe degree of hydrolysis for the particular material of that example.Partially hydrolyzed poly(ethylene-co-vinyl acetate) is available fromE. I. du Pont de Nemours & Co., Inc. Wilmington, Del., United States ofAmerica under the trademark designation, Elvon PIS-7802 hydroxyvinylresin.

This example utilizes poly(ethylene-covinyl acetate) which is about50-53 percent hydrolyzed, 3.12 grams of which is dissolved inmilliliters of toluene to yield a solution of the capsule wall-formingmaterial. The solution is heated to 5060 C. and the following are addedwith continued agitation: 125 milliliters of a 50 percent, by weight,solution of polydimethyl siloxane in toluene to serve as thecomplementary phase-separation-inducing polymeric material and 30milliliters of glycerol with a small amount of a colored crystal violetsalt dissolved therein to serve as the capsule core or internal phasematerial. An example of the polydimethyl siloxane used herein is L-45(trademark) silicon fluid having a viscosity of about 500 centistokesand sold by Union Carbide Corporation, New York, N.Y., United States ofAmerica. After addition of the above materials, a three-phase system exists as afore-described, including: a continuous phase of toluene havinga major amount of the siloxane and some of the capsule wall materialdissolved therein, a discontinuous phase of droplets of the blue-coloredglycerol as intended capsule core material and a discontinuous phase ofliquid, phaseseparated, droplets of a concentrated solution of thecapsule wall material in toluene;said capsule wall material dropletswetting and enwrapping the capsule core entities to yield embryoniccapsules. The system, at this point, then, has already yielded capsulesof a liquid-walled nature containing a polar liquid. Agitation iscontinued while the system is permitted to cool to room temperature.

As a test, 50 milliliter portions of the cooled capsule containingsystem are treated by adding toluene diisocyanate in amounts from 0.5milliliter to 4 milliliters and the portions are stirred at roomtemperature for about 16 hours. Agitation is stopped, the supernatant isremoved, the capsules are washed with hexane and then with water and arethen dried. The resulting capsules do not agglomerate and they releasebluecolored glycerol on rupture. The capsules, left in ambientconditions, do not appear to exude the glycerol internal phase.

EXAMPLE II This example uses the same capsule wall material as that usedin Example I, above. 5 grams of the capsule wall material is dissolvedin 500 milliliters of toluene at above about 60 C. The solution isplaced in a preheated Waring Blendor (trademark) cup under lowagitation;care being employed with regard to avoiding fire andexplosion. Then, 100 milliliters of an 80/20-glycerol/water solution isadded as a capsule internal phase, the agitation is increased to a rapidrate and is continued for about 5 minutes to obtain a fine dispersion.25 milliliters of cottonseed oil is added as a phase-separation inducerand agitation is continued for 2 minutes at the rapid rate. The systemis then chilled to 25 C. and 200 milliliters of a solution of 5 percent,by weight, Mondur CB-75 (trademark) in toluene is added to cross-linkand chemically harden the capsule wall material. Mondur CB-75 is atoluene diisocyanate adduct of trimethanol propane and is sold by theMobay Chemical Company, Pittsburgh, Pa., United States of America. Thesystem is stirred at low rate for a few hours at room temperature andthen for about 10 hours at about 45 C. The capsules can then be coatedonto paper or isolated as a liquidcontaining powder. The individualcapsules from this example are about 5 to 20 microns in averagediameter.

EXAMPLE III This example is performed identically with Example II,above, with the exceptions that tetrachloroethylene is substituted,volume-for-volume for the toluene of that example and the capsule wallmaterial is hardened by reaction with toluene diisocyanate instead ofthe toluene diisocyanate adduct of that example. The individual capsulesfrom this example are about 5 to 20 microns in average diameter.

EXAMPLE IV Examples I and II are repeated using a liquid polybutadieneas the complementary phase separation inducer. Capsule size can beregulated somewhat by control of the degree of agitation, the ratio ofthe degree of agitation, the ratio of capsule wall material to capsuleinternal phase material, the temperature of the system and the like.

EXAMPLE v 10 grams of the poly(ethylene-co-vinyl acetate) which is 43 to53 percent hydrolyzed is dissolved in 500 milliliters oftrichloroethylene and cooled to about 10 to 15 C. Into that solution isdispersed about 100 milliliters of capsule core material (water,glycerol, etc., l00 grams of the material if it is a solid) and about 90milliliters of cottonseed oil is added to serve asphase-separation-inducing material. Embryonic capsules are thus formedand the embryonic capsule walls are chemically hardened by adding 50milliliters of a 20 percent, by weight, solution of Mondur CB-75(trademark) in trichloroethylene to the capsule-containing system andstirring overnight. The capsules are isolated by decanting the capsulemanufacturing liquid, washing the capsules with trichloroethylene anddrying them by evaporating the trichloroethylene. The hardened andisolated capsules appeared of high quality with little tendency towardexudation of the capsule contents.

EXAMPLE VI As a test, 10 grams of the poly(cthylene-co-vinyl acetate)which was 38 percent hydrolyzed, was dissolved in 600 milliliters oftoluene and into that solution was dispersed 70 milliliters of an/20-glycerol/water solution to serve as capsule core material and 50milliliters of cottonseed oil to serve as phase-separation-inducingmaterial. The temperature during this agitation and dispersing rangedfrom about 45 to about 25 C. On addition of the cottonseed oil, a phaseseparation of the capsule wall material did occur and embryonic capsulesdid form, but the separated phase was not adequately viscous for goodcapsule manufacture and the separated phase did not wrap the capsulecore droplets well. Nevertheless, 5 milliliters of the Mondur CB-75(trademark), above-mentioned, and 5 milliliters of toluene diisocyanatewere added to harden the capsule walls and completed capsules wereobtained after stirring the system for about 16 hours. The capsules wereisolated by decanting the manufacturing liquid, washing the capsuleswith toluene and drying them by evaporating the toluene. The capsulesobtained in this example were not of high quality but would be usable insome instances.

EXAMPLE VII This example was conducted identically with that of ExampleVI, above, with the exception that the poly(ethylene-covinyl acetate)was about 43 percent hydrolyzed. The separated phase of capsule wallmaterial in this example was of the proper viscosity and wetted andwrapped the capsule core entities very well to yield embryonic capsulesof high quality. The hardened and isolated capsules appeared of highquality with little tendency toward exudation of the capsule contents.

EXAMPLE VIII To continue the tests of Examples VI and VII, this examplewas conducted identically with those above, but using poly(ethylene-co-vinyl acetate) which was about 505 3% hydrolyzed. Thecapsules of this example were of high quality substantially identicalwith those of Example VII, above.

EXAMPLE IX In a continuation of the test, the same technique as abovewas followed but using poly(ethylene-co-vinyl acetate) which was about54 percent hydrolyzed. The separated phase of capsule wall material inthis example was highly viscous and exhibited some difficulty inwrapping the capsule core material. Capsules of a fair quality wereisolated, however.

EXAMPLE X As a last part of the test an encapsulation attempt was madeusing poly(ethylene-co-vinyl acetate) which was 56 percent hydrolyzed.The separated phase was stringy and semi-solid and would not wrap aroundintended capsule cores to yield capsules.

The example was repeated using poly(ethylene-co-vinyl acetate) which was56 percent hydrolyzed and again with material which was 59 percenthydrolyzed. In both cases the separated phase was substantially solidand did not yield capsules.

It is important to note that in all of the poly(ethylene-covinylacetate) materials used in the above examples, the molecular weightswere substantially the same;the differences in behavior of the variousseparated liquid phases being due entirely to differences in degree ofhydrolysis.

EXAMPLE XI This example is performed similarly with any of the aboveexamples which resulted in acceptable capsules with the exception thatthe capsule wall hardening material is sodium methoxide supplied as 20milliliters of a 0.1 Normal solution in l/lO-methanol/benzene. Theresulting capsules can be coated onto a substrate to dry or can beisolated by decanting the manufacturing liquid, washing the capsuleswith petroleum ether and drying.

EXAMPLES XII-XVI The test of Examples VI-X, above, is repeated using 60milliliters of a 70/30-glycerol/formamide solution in place of theglycerol/water solution as capsule core material. The test results aresubstantially the same herein as in Examples VI-X.

EXAMPLE XVII Example VIII, above, is repeated but using 70 millilitersof 50 percent, by weight, aqueous solution of acetamide as capsule corematerial in place of the glycerol/water solution. Capsules of highquality are manufactured.

EXAMPLE XVIII Example VIII, above, is repeated but using 70 millilitersof a 3 percent, by weight, solution of oxamide in 70 percent, by weight,aqueous glycerol solution. Capsules of high quality are manufactured.

EXAMPLE XIX Example VIII, above, is repeated but using 50 milliliters ofa 4 percent, by weight, solution of malonyl chloride in toluene as thecapsule wall hardening material in place of the Mondur CB-75" and thetoluene diisocyanate. In using this diacid chloride hardening material,the capsules need only be stirred for about 30 minutes before isolation.Capsules of high quality are manufactured.

What is claimed is:

1. In a process of forming minute capsules, en masse, which comprisesestablishing an agitated system consisting of a liquid vehicleconstituting a major portion of the system by volume and forming acontinuous liquid first phase, a second phase dispersed therein,consisting of minute mobile entities of capsule core material, and athird phase dispersed therein constituting a minor but significantportion of said system by volume, and consisting of minute mobile liquidentities of a wall-forming solution of a hydrophobic polymeric material,the capsule core material being wettable by said wall-forming solutionand the three phases being mutually immiscible, whereby saidwall-fomring solution deposits on and around the capsule core entitiesto form a protective wall:

the improvement which comprises utilizing, as the hydrophobic polymericmaterial, poly(ethylene-co-vinyl acetate) having the vinyl acetategroups hydrolyzed to vinyl alcohol groups in the amount of 38 to 55percent. 2. The process of claim 1 wherein, of the poly(ethylene-covinylacetate), ethylene groups constitute 70 to percent of the total polymergroups present.

3. In a process of forming minute capsules, en masse, which comprises:(a) establishing an agitated system consisting of a liquid vehicleconstituting a major portion of the system by volume and forming acontinuous liquid first phase, a second phase dispersed therein,consisting of minute mobile entities of capsule core material, and athird phase dispersed therein constituting a minor but significantportion of said system by volume, and consisting of minute mobile liquidentities of a wall-forming solution of a hydrophobic polymeric material,said three phases being mutually immiscible, whereby said wall-formingsolution deposits on and around the capsule core entities to form aprotective wall, and (b) hardening the walls so formed:

the improvement which comprises utilizing, as the hydrophobic polymericmaterial, poly(ethylene-covinyl acetate) having the vinyl acetate groupshydrolyzed to vinyl alcohol groups in the amount of 38 to 55 percent.

4. The process of claim 3 wherein, of the poly(ethylene-covinylacetate), ethylene groups constitute 70 to 85 percent of the totalpolymer groups present.

5. The process of claim 3 wherein hardening the protective wall isaccomplished by reaction with a treatment material selected from thegroup of materials consisting of diisocyanates, polyisocyanates anddiacid chlorides.

6. The process of claim 3 wherein hardening the protective wall isaccomplished by reaction with an alkali alkoxide.

7. A three-phase capsule-forming system capable of forming minutecapsules en masse, consisting essentially of a. a liquid vehicleconstituting a major portion of the system by volume and forming acontinuous liquid first phase,

b. a second phase dispersed therein constituting a minor but significantportion of said system by volume, consisting of minute discrete liquidentities of a wall-forming solution of poly(ethylene-co-vinyl acetate)having from 38 to 55 percent of the vinyl acetate groups hydrolyzed tovinyl alcohol groups, and a third phase dispersed therein constitutingthe remainder of the system, by volume, consisting of minute discreteentities of capsule core material, the core material being wettable bysaid wall-forming solution and the said three phases being mutuallyimmiscible.

8. The three-phase system of claim 7 wherein the mo] percent of ethylenein the poly( ethylene-co-vinyl acetate) is about 70 to 85 percent.

2. The process of claim 1 wherein, of the poly(ethylene-co-vinylacetate), ethylene groups constitute 70 to 85 percent of the totalpolymer groups present.
 3. In a process of forming minute capsules, enmasse, which comprises: (a) establishing an agitated system consistingof a liquid vehicle constituting a major portion of the system by volumeand forming a continuous liquid first phase, a second phase dispersedtherein, consisting of minute mobile entities of capsule core material,and a third phase dispersed therein constituting a minor but significantportion of said system by volume, and consisting of minute mobile liquidentities of a wall-forming solution of a hydrophobic polymeric material,said three phases being mutually immiscible, whereby said wall-formingsolution deposits on and around the capsule core entities to form aprotective wall, and (b) hardening the walls so formed: the improvementwhich comprises utilizing, as the hydrophobic polymeric material,poly(ethylene-co-vinyl acetate) having the vinyl acetate groupshydrolyzed to vinyl alcohol groups in the amount of 38 to 55 percent. 4.The process of claim 3 wherein, of the poly(ethylene-co-vinyl acetate),ethylene groups constitute 70 to 85 percent of the total polymer groupspresent.
 5. The process of claim 3 wherein hardening the protective wallis accomplished by reaction with a treatment material selected from thegroup of materials consisting of diisocyanates, polyisocyanates anddiacid chlorides.
 6. The process of claim 3 wherein hardening theprotective wall is accomplished by reaction with an alkali alkoxide. 7.A three-phase capsule-forming system capable of forming minute capsulesen masse, consisting essentially of a. a liquid vehicle constituting amajor portion of the system by volume and forming a continuous liquidfirst phase, b. a second phase dispersed therein constituting a minorbut significant portion of said system by volume, consisting of minutediscrete liquid entities of a wall-forming solution ofpoly(ethylene-co-vinyl acetate) having from 38 to 55 percent of thevinyl acetate groups hydrolyzed to vinyl alcohol groups, and c. a thirdphase dispersed therein constituting the remainder of the system, byvolume, consisting of minute discrete entities of capsule core material,the core material being wettable by said wall-forming solution and thesaid three phases being mutually immiscible.
 8. The three-phase systemof claim 7 wherein the mol percent of ethylene in thepoly(ethylene-co-vinyl acetate) is about 70 to 85 percent.